1. Field of the Invention
The present invention relates to a metal wiring for a semiconductor device, and more particularly to a metal wiring for a semiconductor device having improved electro-migration characteristics and a method for forming the same.
2. Discussion of the Related Art
Metal wirings for semiconductor devices are primarily made of aluminum due to its high electrical conductivity, its excellent adhesion to an oxide film, and its malleability. However, aluminum has several problems, such as a difficulty in electric migration, hillocks, and spikes, and therefore is limited in its use.
Accordingly, materials of the metal wirings having high conductivity, such as copper (Cu), gold (Au), silver (Ag), cobalt (Co), chrome (Cr), and nickel (Ni), have been researched. Among the above materials, copper (Cu) has low specific resistance, excellent reliability, and low production costs and is therefore widely used.
However, since copper cannot be easily patterned, it is difficult to form a metal wiring made of copper using a conventional method. Accordingly, a damascene structure in which a metal wiring is produced by forming trenches in an insulating film and filling the trenches with copper is employed. Particularly, a dual damascene structure in which the trenches and via holes are simultaneously formed in the insulating film is employed. A conventional metal wiring structure having a dual damascene structure is shown FIG. 1.
As shown in FIG. 1, an interlayer insulating film 20 is formed on a first insulating layer 10. Via holes and trenches having a width larger than that of the via holes are formed in the interlayer insulating film 20. A barrier metal layer 30, a copper seed layer 32, and a copper layer 34 are sequentially formed in the via holes and the trenches of the interlayer insulating film 20. A capping layer 40 is formed on the overall surface of the interlayer insulating film 20, and a second insulating layer 50 is formed on the capping layer 40. The capping layer 40 is made of an insulating film, such as an oxide film or a nitride film.
In the above metal wiring structure having the damascene structure, resistance at an interface point B, between the capping layer 40 and the copper layers 32 and 34, is higher than resistance at an interface point A, between the barrier metal layer 30 and the copper layers 32 and 34. Accordingly, there is a current flow difference, and electro-migration characteristics at the interface between the capping layer 40 and the copper layers 32 and 34 are deteriorated.